The overall objectives of this project are to define the heterogeneity of cells and cell functions involved in the regulation of immune responses. During the next project year the major goal will be to study the functions of accessory cells in several in vitro systems. A second area of investigaton has been to develop new methods for studying T cell heterogeneity. The goal of a third project is to develop suitable in vitro conditions for studying the role of antiserum in blocking cell mediated cytotoxicity ("enhancement"). Bibliographic references: Miller, C.L., and Mishell, R. I., Differential regulatory effects of accessory cells on the generation of cell-mediated immune reactions. J. Immunol., 114: 692, 1975. Ly, I.A., and Mishell, R.I., Separation of mouse spleen cells by passage through columns of Sephadex G-10. J. Immunol. Meth., 5: 239-247, 1974.